Why we celebrate Thanksgiving every year. It isn’t what you think.

(There is an enormous amount of misinformation about the origins of the Thanksgiving holiday as we celebrate it today — including when, how and why it became a tradition in the United States. Here’s the real story, which I published a few years ago and am doing so again.)

What Americans think they know about the history of Thanksgiving doesn’t always square with the truth.

For example, it is generally believed that in 1621, the Pilgrims invited Wampanoag Indians to a feast in Plymouth Colony to celebrate their first harvest, and a good time, with turkey and pumpkin pie, was had by all. Well, maybe, and maybe not.

Historians, including those at Plimoth Plantation, a living museum in Plymouth, Mass., say that they do know there was a feast that year shared by the colonists and Wampanoag Indians, and Squanto, who had learned English, served as translator. But the one historical account of the actual dinner says venison was served and some sort of fowl, but it doesn’t specifically mention turkey. Pumpkin was available, but it is not likely the colonists whipped up a pie. Furthermore, sweet potatoes were unknown to the colonists, and cranberries may have been served but not as a relish.

There’s a lot of misinformation about the Pilgrims, too. American kids learn that the Pilgrims came to the New World in search of religious freedom, and they dressed only in black and white, and wore buckles on their shoes. No, no, and no.

The Pilgrims left Britain in search of religious freedom, but found it in Holland in the early 1600s, where they found a high degree of religious tolerance. The reason they wanted to come to the New World and establish a colony was to preserve their English identity and for economic reasons. Also, they didn’t wear buckles on their shoes, and Pilgrim women dressed in colors, including red, green, blue and violet, while men wore a variety of colors, too.

If you think Americans have been celebrating Thanksgiving annually since 1621, guess again. Nobody at the time thought of it as the start of a new tradition, and there had been similar gatherings elsewhere earlier. Historians know there was another feast in the colony in 1623 — but it was held earlier in the year. Different colonies celebrated their own days of thanksgiving during the year.

In 1789, George Washington declared Thursday, Nov. 26, a Thanksgiving holiday, but only for that year, and it wasn’t connected to the Pilgrim feast but rather intended as a “public thanksgiving and prayer” devoted to “the service of that great and glorious Being who is the beneficent Author of all the good that was, that is, or that will be.”

Enter a 19th century author, poet and magazine editor named Sarah Josepha Hale. She was editor of the influential Godey’s Lady’s Book for 40 years, from 1837 to 1877, when she was nearly 90 years old. She and her husband David Hale had five children, and when he died in 1822, she wore black for the rest of her life. Hale was an education advocate and, through the magazine she edited, became a famous figure in the country who set fashion, reading and cooking trends. Washington Irving Jr., Nathaniel Hawthorne and Oliver Wendell Holmes were among the authors who published work in her magazine. She was also a prolific author, writing dozens of novels and books of poetry, and penned (or co-penned, according to one account) the famous “Mary Had a Little Lamb,” which was published in 1830.

Hale, who was highly patriotic, read about the 1621 feast of the Pilgrims and became captivated with the idea of turning it into a national holiday. She published in the Godey’s Lady’s Book recipes for turkey and stuffing and pumpkin pie and started traditions that had nothing to do with the colonists. She began a lobbying campaign to persuade President Abraham Lincoln to make Thanksgiving an official annual holiday, using her magazine to build public support by writing an editorial every year starting in 1846. She also sent letters to all governors in the United States and territories. In 1863, Lincoln did set Thanksgiving as an official holiday to be celebrated on the fourth Thursday of November every year.

In 1939, President Franklin D. Roosevelt agreed to move the annual Thanksgiving holiday to the third Thursday of November. Why? To help the economy by making the Christmas shopping season a little bit longer. There was so much opposition to the move that two years later he changed it to the fourth Thursday in November.

Then there’s the myth of how the presidential pardon of a turkey started with Abraham Lincoln when his son begged his dad to save the animal. Actually, it didn’t. The tradition goes all the way back in history to … 1989, when President George H.W. Bush officially pardoned the first one. According to a perhaps apocryphal story, in 1863, Lincoln’s 10-year-old son, Tad, supposedly became fond of a turkey given to the family for a holiday feast. Tad named the turkey Jack and begged his father to save the animal. Lincoln did. The only problem with that as a Thanksgiving story is that Tad’s plea was to save the Christmas turkey!

At the 67th anniversary of the National Thanksgiving Turkey presentation on Wednesday, President Obama pardoned two Ohio turkeys that will now live at the home of a former Virginia governor. (AP)

And, finally, you may hear people say that turkey makes them tired. No, it doesn’t. Turkey contains tryptophan, an essential amino acid that is thought to have a sedative effect. As it turns out, turkey doesn’t have any more tryptophan than other foods, including chicken, and even if tryptophan did induce tiredness, there isn’t enough in turkey to do so. So if you are tired after eating Thanksgiving dinner, don’t blame the turkey.